(1) Field of the Invention
The invention relates to network communications. More specifically, the invention relates to synchronization between a frame or in a subdelineation unit.
(2) Background
Two common types of framers are in common use in network communications. A T1 framer is used with T1 communications and generates a framing bit every 193 bits. This framing bit permits a cell delineation unit to identify octet boundaries for an incoming data stream. A single line digital subscriber line (SDSL) framer does not generate a framing bit. Typically, synchronization for SDSL uses serial bit synchronization to perform synchronization on a bit by bit basis. However, in some cases, it is desirable to perform octet aligned synchronization. Absent a framing bit, a cell delineation unit has only a one in eight chance of being in octet aligned synchronization with an SDSL framer. This is particularly problematic in the context of an asynchronous link between the framer and an endpoint from which the data originates. Thus, the problem arises in a context of the system which communicates using asynchronous transfer mode (ATM) cells to communicate between a pair of end points how to assure synchronization when it is unknown whether the remote framer is a T1 framer or an SDSL framer.
A method and apparatus for synchronizing ATM cells is disclosed. A synchronization unit receives a data clock signal and a plurality of control signals. Based on those signals, a sync pulse is generated. If synchronization is not achieved within a predetermined time period, the sync pulse is shifted one bit location. Through iterative shifting of the sync pulse, synchronization is ultimately achieved.